The structure used in the spin lock implementation of a read-write lock. More...

#include <sync0rw.h>

Inheritance diagram for rw_lock_t:

Public Member Functions
	rw_lock_t ()=default

	rw_lock_t (const rw_lock_t &)=delete
	rw_lock_t is not a copyable object, the reasoning behind this is the same as the reasoning behind why std::mutex is not copyable. More...

rw_lock_t &	operator= (const rw_lock_t &)=delete

	UT_LIST_NODE_T (rw_lock_t) list
	All allocated rw locks are put into a list. More...

	~rw_lock_t () override
	Destructor. More...

virtual std::string	to_string () const override
	Print the rw-lock information. More...

virtual std::string	locked_from () const override
	Print where it was locked from. More...

	UT_LIST_BASE_NODE_T (rw_lock_debug_t) debug_list
	In the debug version: pointer to the debug info list of the lock. More...

Public Member Functions inherited from latch_t
	latch_t (latch_id_t id=LATCH_ID_NONE) 1
	Constructor. More...

latch_t &	operator= (const latch_t &)=default

virtual	~latch_t () 1
	Destructor. More...

latch_id_t	get_id () const

bool	is_rw_lock () const 1

latch_level_t	get_level () const 1

bool	is_temp_fsp () const 1

void	set_temp_fsp () 1
	Set the temporary tablespace flag. More...

const char *	get_name () const 1

Public Attributes
std::atomic< int32_t >	lock_word
	Holds the state of the lock. More...

std::atomic< bool >	waiters
	1: there are waiters More...

std::atomic< bool >	recursive
	Default value FALSE which means the lock is non-recursive. More...

bool	writer_is_wait_ex
	This is TRUE if the writer field is RW_LOCK_X_WAIT; this field is located far from the memory update hotspot fields which are at the start of this struct, thus we can peek this field without causing much memory bus traffic. More...

volatile ulint	sx_recursive
	number of granted SX locks. More...

std::atomic< os_thread_id_t >	writer_thread
	Thread id of writer thread. More...

os_event_t	event
	Used by sync0arr.cc for thread queueing. More...

os_event_t	wait_ex_event
	Event for next-writer to wait on. More...

const char *	cfile_name
	File name where lock created. More...

const char *	last_s_file_name
	last s-lock file/line is not guaranteed to be correct More...

const char *	last_x_file_name
	File name where last x-locked. More...

uint16_t	cline
	Line where created. More...

bool	is_block_lock
	If 1 then the rw-lock is a block lock. More...

uint16_t	last_s_line
	Line number where last time s-locked. More...

uint16_t	last_x_line
	Line number where last time x-locked. More...

uint32_t	count_os_wait
	Count of os_waits. More...

struct PSI_rwlock *	pfs_psi
	The instrumentation hook. More...

uint32_t	magic_n = {MAGIC_N}

latch_level_t	level
	Level in the global latching order. More...

Public Attributes inherited from latch_t
latch_id_t	m_id
	Latch ID. More...

bool	m_rw_lock
	true if it is a rw-lock. More...

bool	m_temp_fsp
	true if it is an temporary space latch More...

Static Public Attributes
static const uint32_t	MAGIC_N = 22643
	For checking memory corruption. More...

Detailed Description

The structure used in the spin lock implementation of a read-write lock.

Several threads may have a shared lock simultaneously in this lock, but only one writer may have an exclusive lock, in which case no shared locks are allowed. To prevent starving of a writer blocked by readers, a writer may queue for x-lock by decrementing lock_word: no new readers will be let in while the thread waits for readers to exit.

Constructor & Destructor Documentation

◆ rw_lock_t() [1/2]

rw_lock_t::rw_lock_t ( )

default

◆ rw_lock_t() [2/2]

rw_lock_t::rw_lock_t ( const rw_lock_t & )

delete

rw_lock_t is not a copyable object, the reasoning behind this is the same as the reasoning behind why std::mutex is not copyable.

It is supposed to represent a synchronization primitive for which copying semantics do not make sense.

◆ ~rw_lock_t()

rw_lock_t::~rw_lock_t ( )

inlineoverride

Destructor.

Member Function Documentation

◆ locked_from()

std::string rw_lock_t::locked_from ( ) const

overridevirtual

Print where it was locked from.

Returns: the string representation

Implements latch_t.

◆ operator=()

rw_lock_t& rw_lock_t::operator= ( const rw_lock_t & )

delete

◆ to_string()

std::string rw_lock_t::to_string ( ) const

overridevirtual

Print the rw-lock information.

Returns: the string representation

Implements latch_t.

◆ UT_LIST_BASE_NODE_T()

rw_lock_t::UT_LIST_BASE_NODE_T ( rw_lock_debug_t )

In the debug version: pointer to the debug info list of the lock.

◆ UT_LIST_NODE_T()

rw_lock_t::UT_LIST_NODE_T ( rw_lock_t )

All allocated rw locks are put into a list.

Member Data Documentation

◆ cfile_name

const char* rw_lock_t::cfile_name

File name where lock created.

◆ cline

uint16_t rw_lock_t::cline

Line where created.

◆ count_os_wait

uint32_t rw_lock_t::count_os_wait

Count of os_waits.

May not be accurate

◆ event

os_event_t rw_lock_t::event

Used by sync0arr.cc for thread queueing.

◆ is_block_lock

bool rw_lock_t::is_block_lock

If 1 then the rw-lock is a block lock.

◆ last_s_file_name

const char* rw_lock_t::last_s_file_name

last s-lock file/line is not guaranteed to be correct

◆ last_s_line

uint16_t rw_lock_t::last_s_line

Line number where last time s-locked.

◆ last_x_file_name

const char* rw_lock_t::last_x_file_name

File name where last x-locked.

◆ last_x_line

uint16_t rw_lock_t::last_x_line

Line number where last time x-locked.

◆ level

latch_level_t rw_lock_t::level

Level in the global latching order.

◆ lock_word

std::atomic<int32_t> rw_lock_t::lock_word

Holds the state of the lock.

◆ MAGIC_N

const uint32_t rw_lock_t::MAGIC_N = 22643

static

For checking memory corruption.

◆ magic_n

uint32_t rw_lock_t::magic_n = {MAGIC_N}

◆ pfs_psi

struct PSI_rwlock* rw_lock_t::pfs_psi

The instrumentation hook.

◆ recursive

std::atomic<bool> rw_lock_t::recursive

Default value FALSE which means the lock is non-recursive.

The value is typically set to TRUE making normal rw_locks recursive. In case of asynchronous IO, when a non-zero value of 'pass' is passed then we keep the lock non-recursive.

This flag also tells us about the state of writer_thread field. If this flag is set then writer_thread MUST contain the thread id of the current x-holder or wait-x thread. This flag must be reset in x_unlock functions before incrementing the lock_word

◆ sx_recursive

volatile ulint rw_lock_t::sx_recursive

number of granted SX locks.

◆ wait_ex_event

os_event_t rw_lock_t::wait_ex_event

Event for next-writer to wait on.

A thread must decrement lock_word before waiting.

◆ waiters

std::atomic<bool> rw_lock_t::waiters

1: there are waiters

◆ writer_is_wait_ex

bool rw_lock_t::writer_is_wait_ex

This is TRUE if the writer field is RW_LOCK_X_WAIT; this field is located far from the memory update hotspot fields which are at the start of this struct, thus we can peek this field without causing much memory bus traffic.

◆ writer_thread

std::atomic<os_thread_id_t> rw_lock_t::writer_thread

Thread id of writer thread.

Is only guaranteed to have non-stale value if recursive flag is set, otherwise it may contain native thread handle of a thread which already released or passed the lock.

The documentation for this struct was generated from the following files:

storage/innobase/include/sync0rw.h
storage/innobase/sync/sync0rw.cc

Public Member Functions

Public Attributes

Static Public Attributes